This invention relates generally to fluid treatment and, more particularly, but not solely, to a system for sterilising water or sewage.
Untreated sewage is often pumped into the sea and rivers. This sewage may contain harmful micro-organisms and bacteria such as hepatitis, which can pass into the food chain and which can also be passed on to people who come into contact with the polluted water.
It is well known that high-intensity ultra-violet (UV) light has germicidal properties which can be used to sterilise water. Water treatment companies are reluctant to utilise UV sterilisers because they do not effectively treat all of the water. This occurs because conventional ultra-violet (UV) light fluid treatment apparatus only operate effectively if the fluid being treated is optically clear. For example, if the fluid being treated is cloudy or of high turbidity, the UV light is substantially attenuated away from the close proximity of the light source, thus clumps of microbes which do not come within close proximity of the UV light source do not receive a dose of UV radiation which is sufficient to kill them. Furthermore, microbes tend to collect in clumps, thus microbes at the centre of the clumps are shaded from the UV light by the microbes on the outside of the clump.
U.S. Pat. No. 5,675,153 discloses a fluid treatment apparatus comprising an elongate tubular duct having inlet and outlet ports at or adjacent its opposite ends, an elongate light source extending along a longitudinal axis of the duct and a guide vane extending helically along the internal wall of the duct between said inlet and outlet ports. Radially-extending slots are formed in the guide vane for communicating between adjacent turns of the fluid flow passage defined by the vane.
In use, fluid to be treated flows through the duct from the inlet port to the outlet port along the helical passage defined by the guide vane. This helical flow generates controlled turbulence which ensures that all of the water or other fluid being treated comes within close proximity of the light source during treatment. Fluid flowing along the passage is able to pass through the slots between adjacent turns of the helical passage. As clumps of microbes pass through the slots, they are broken up into individual microbes which can be treated more effectively.
The guide vane is formed by welding a series of small rectangular pieces of metal along a helical line, which is scribed on the wall of the tubular duct. The small rectangular pieces of metal are precisely twisted at their opposite ends prior to attachment to the tubular duct and the grain of the pieces of metal used to form the segments encourages the pieces to adopt the correct shape.
A disadvantage of the above-mentioned fluid treatment apparatus is that it is complicated and time consuming to construct, particularly since the segments are difficult to insert at the centre of the elongate tubular duct.
We have now devised a fluid treatment apparatus which alleviates the above-mentioned problems.
In accordance with this invention, there is provided a fluid treatment apparatus comprising:
a duct portion having an elongate tubular duct;
inlet and outlet ports at or adjacent opposite ends of the duct;
a separate vane portion, mounted internally of the duct and carrying a helical guide vane, which extends longitudinally of the duct between said inlet and outlet ports and which promotes a helical fluid flow therebetween; and
an elongate light source extending longitudinally of the duct.
The helical guide vane is formed on the vane portion of the apparatus, which is then inserted into the duct of the duct portion. It will be appreciated that the apparatus is thus much easier to assemble than the apparatus disclosed in U.S. Pat. No. 5,675,153, since the helical guide vane is formed prior to insertion into duct.
Preferably, apertures are formed in the helical guide vane for communicating between adjacent turns thereof.
Preferably, the helical guide vane extends around an elongate support, which extends longitudinally of the duct.
Preferably, at least one end of the elongate support is engaged with an end wall of the duct.
Preferably the or each end wall with which the support is engaged is provided on said vane portion of the apparatus.
Preferably the helical guide vane is formed by attaching individual segments of the vane to the surface of the longitudinally-extending support.
Preferably the individual vane segments are pre-shaped prior to attachment, so that when assembled the segments define a helix.
Preferably, a plurality of circumferentially-spaced elongate light sources extend longitudinally of the duct.
Preferably, the or each light source extends through adjacent turns of the guide vane.
In one embodiment, the radially outer edge of the guide vane abuts the internal surface of the tubular duct, so that fluid can only flow on a helical path between the inlet and outlet ducts.
In an alternative embodiment, the radially outer edge of the guide vane is spaced from the internal surface of the tubular duct, so that fluid can flow on an axial as well as helical path between the inlet and outlet ducts. The fluid flows of the two paths interfere to produce a swirling flow of fluid which moves helically along the duct. This swirling action further increases the turbulence inside the duct, moving the water in a controlled double helix action.
Preferably, the vane portion carries a plurality of parallel-extending helical guide vanes.
These and other objects, features and advantages of the present invention will be clearly understood through consideration of the following detailed description.